The invention relates to transport and guide arrangements of the conveyor-belt type, particularly for use with photographic and x-rays apparatuses, for transporting flexible sheet material of the type which, for one reason or another, is to be physically contacted by the transporting means only at its lateral edge portions and not on either of its two faces.
More particularly, the invention relates to such arrangements wherein each edge portion of the sheet material is engaged from opposite sides by narrow conveyor belts which effect the desired transport, with such pairs of cooperating conveyor belts being trained about pairs of driven guide rollers or pulleys.
In many circumstances in photography, copying and related fields, sheet material, such as photosensitive copy paper, coated copy paper, polyester webs or x-ray film, must be transported in such a way that only the edge portions of the sheet material are physically engaged by the conveying means, with the major surface portions of both sides of the sheet material not being physically contacted by conveying or other structure. Usually, the sheet material can be transported in this way by using narrow conveyor belts arranged in pairs with the conveyor belts of each pair engaging the associated edge portion of the sheet material from respective opposite sides. The sheet material will then be transported along the path of travel of the conveyor belts.
With known transport arrangements of this type, the sheet material being conveyed may bulge at its central portion, particularly when travelling around a deflection or guide roller or pulley, due to the inherent weight of the sheet material. Even when travelling along straight-line sections of the travel path, the sheet material being conveyed may sag in the middle due to its inherent weight and/or bulges may develop in the material for the same reason as are involved with travel of the material along curved sections of the path.
if the sheet material deviates from its proper planar shape serious problems may result. In some circumstances the sheet material must be made to exactly occupy a certain plane for optical reasons. As another example, a feeding device in the processing apparatus may engage the leading (transverse) edge of the sheet material, so that if this edge is not prefectly straight a malfeed may occur.
Commonly owned U.S. Pat. No. 3,836,060 discloses a copying apparatus for long strips of copying material. The unexposed copying material is transported in front of a copying window and while in that position is subjected to tension in the longitudinal direction. This tensioning of the strip results from the pinching of the strip between the two cooperating transport cylinders located upstream of the copying window, on the one hand, and, on the other hand, from the provision, somewhat downstream of the copying window, of a frictional engaging element. The frictional engaging element engages a portion of the strip downstream of the copying window and urges it downstream, so as to tighten and flatten out the portion of the strip located at the copying window. However, the tensioning arrangement disclosed in that patent can only be used to effect tensioning in the longitudinal direction, because the pinching rollers cannot be arranged to establish a tension in direction transverse to the strip transport direction. Also, with the arrangement disclosed in that patent, it is not possible to tension the strip during strip transport.